Electric fuses



p 8, 1964 J. FEENAN ETAL 3,148,257

ELECTRIC FUSES Filed Nov. 18, 1960 4 Sheets-Sheet 1 FIG. 10

INVENTORS: JOHN mmmn ERIC JACKS VERNON BRANDON BETTERIDGE y Si va... BM WW Sept. 8, 1964 FEENAN ETAL 3,148,257

ELECTRIC FUSES Filed NOV 18, 1960 4 Sheets-Sheet 2 FIG. 3

INVENTORS: JOHN FEENAN ERIC JACKS VERNON BRANDON BETTERIDGE Attorneys J. FEENAN ETAL Sept. 8, 1964 ELECTRIC FUSES 4 Sheets-Sheet 3' Filed NOV-- 18, 1960 INVWIDRS: JOHN FmA-N ERIC JACKS VERNON BRANDON BETTERIDGE S )HM, )MJ

Attorneys United States Patent C) 3,148,257 ELECTRIC FUES John Feen'an, Erie Jacks, and Vernon Brandon Betteridge, Liverpool, England, assignors to The English Electric Company Limited, London, England, a British company Filed Nov. 18, 1960, Ser. No. 70,230 Claims priority, application Great Britain, Nov. 27, 1959, 40,404/59, 40,405/59; Feb. 17, 1960, 5,553/60, 5,554/60 3 Claims. (Cl. 200-435) This invention relates to electrical fuse-elements and fuse-links.

A fuse-element according to the invention comprises a ribbon of fusible metal, of uniform width, and having a series of grooves each of which extends across the full width of the ribbon; said n'bbon having also, at one end of said series of grooves, a transverse trough which extends across the full width of the ribbon, said trough being filled with metal of lower melting point than, and capable of alloying with, the metal of the ribbon.

According to a preferred feature of the invention, a cartridge fuse-link comprises a tubular insulating container, two conductive members secured to said container one at each end thereof, at least one fuse-element, of the kind described in the preceding paragraph, located by said conductive members and extending between them inside and along the length of said container, and a filling of arcquenching material, said conductive members being in good electrical and heat-conductive connection with the ends of said fuse-element and of large heat capacity relative to said fuse-element.

Further preferred features of the invention will be apparent from the following description and from the ap pended claims.

Fuse-links and fuse-elements which embody the inven tion in preferred form, and -a preferred process for making such fuse-elements, are illustrated in the accompanying drawings in which:

FIG. 1 is a perspective view of a fuse-element,

FIG. 2 is a fragmentary view similar to FlG. 1 with the fuse-element inverted,

FIG. 3 is a fragmentary elevational view of an alternative form of fuse-element,

FIG. 4 is an axial sectional view link,

FIG. 5 is an exploded view of some parts of a cartridge fuse-link,

FIG. 6 is a plan view of the inner end cap of a cartridge fuse-link which is a modification of that shown in FIG. 4,

FIG. 7 is an elevational view of a multiple fuse-element,

FIG. 8 is an elevational view of a high current fuseelement,

FIG. 9 is a view similar to FIG. 4 of a cartridge fuselink which embodies the element shown in FIG. 8, and

FIG. 10 shows the process of rolling sheet material from which fuse-elements of the kind shown in FIGS. 1 and 2 may be cut.

The fuse-element shown in FIG-S. l and 2 consists of a ribbon 10 of silver with a small body 11 of solder fused to it. The ribbon 10 has uniform width. Its thickness is also uniform between the shoulders 12 and 13, except for a series of five grooves 14 spaced at equal intervals from each other along its length. Each of these grooves 14 extends across the full width of the ribbon 10.

At the right hand end of the series of grooves 14-, a trough 15 (shown inverted in FIG. 1) is formed as a partial fold in the ribbon 10 without reduction of its cross section. This trough 15 also extends across the full width of the ribbon 10. The spacing between trough 15 and the nearest of grooves 14 is greater than the spacing between any adjacent pair of the grooves 14.

of a cartridge fuse- The trough 15 is filled with solder 11. The solder 11 is fused on while the ribbon is inverted (as seen in FIG. 2), and the solder therefore fills the trough 15, with a slight meniscus 11a. This method of providing the solder, by melting into a pre-formed trough, gives an ac curate control of the quantity of solder and of the degree to which it becomes alloyed with the silver.

The end portions 16, 17 of fuse-element 10, beyond the shoulders 12 and 13, have greater thickness than the remainder of fuse-element 10.

In a typical example of a fuse-element of the kind shown in FIGS. 1 and 2, but without the thickened end portions 16, 17, intended for use singly in a cartridge for a current-carrying rating of 50 amps at 600 volts, the overall length of the ribbon is 2%. inches and its width of an inch. The thickness o-f the ribbon over the main part of the length, where not reduced, is about 0.01 inch; but at each of the grooves 14 it is reduced to about 0.003 inch. The width of each groove, measured in the direction of the length of the ribbon, is about 0.03 inch at the bottom, but a little Wider at the top because the sides of the grooves are slightly tapered. There are live grooves and the spacing between each one and the next is 0.3 inch.

For other ratings, provided that the voltage does not exceed 600, it is preferred to use different widths of ribbon but to keep all the other dimensions about the same. The preferred ranges for the other dimensions are as follows:

General thickness of ribbon: 0.008 to 0.012 inch.

Thickness of ribbon at bottoms of grooves: 25% to 50% of general ribbon thickness.

Width of grooves, in direction of length of ribbon, at bottom: 0.025 to 0.035 inch.

Spacing between grooves: 0.25 inch to 0.4 inch.

The preferred widths of ribbon range from 0.023 inch for a 15 amp fuse-element to 0.225 inch for a amp fuse-element.

For a 250 volt fuse-element two grooves are sufficient but for higher voltage ratings there should be at least one groove for every 125 volts.

The distance between the solder-filled trough l5 and the nearest of the grooves 14 should, fo the higher voltage ratings, exceed the spacing between grooves; but this is not essential for voltage ratings up to 250 volts.

To avoid introducing unnecessary resistance, and to provide good heat conduction to the terminal members, the overall length of the fuse-element should not be too great. It will not usually be found desirable to use thickor end portions for the fuse-element, in the manner shown at 16, 17 in FIG. 1, unless extra length is needed to satisfy some external dimensional requirement. Where used, these end portions may have thickness about three times the general thickness of the ribbon, so as to keep the overall resistance to a low value.

The trough part of the fuse-element, with the solder fillings, is designed to fuse on sustained moderate overloads, which will not cause fusing at the grooves. Heavy currents such as result from short circuits will, however, fuse the element at all the grooves almost simultaneously.

The solder filled trough is sufficiently spaced from the nearest of the grooves to ensure that the heat generated at the grooves on transient overcurrent up to minimum fusing current will not flow to the trough and substantially alter the fusing characteristics of the trough part of the element. This spacing is also sufficient to prevent the solder from getting into the arcs formed at the grooves under heavy current conditions.

As the grooves extend across the whole width of the ribbon, the groove part of the element is better cooled by conduction than it is in a fuse-element having a fusing portion with reduced width. Wlbn the element fuses at the grooves, a broad but thin arc, with uniform intensity across its width, occurs at each of the series breaks. A steady burn back of the element at each of these breaks is achieved. Good equality of the arcing energy is obtained, both as between the several arcs in one element, and as between the several elements when several are employed in parallel.

FIG. 3 is a fragmentary view of an alternative form of element. This figure shows only the grooved part of the ribbon, and it shows this part with grooves on both faces of the ribbon. In this alternative form also, the ribbon 10 has, on each side of each groove 14 a short portion 18 where the thickness is reduced, though not to the full depth of the groove 14. This feature is especially suitable for a high voltage fuse-element, where considerable length is required. The thickest parts 19 offer low resistance and therefore keep the overall resistance of the element down to a satisfactorily low value. The proportioning of the reduced sections controls the rate of burn back which in turn controls the total are energy and also its distribution within the fuse.

Appropriate dimensions for a fuse-element of the kind shown in FIG. 3 are:

Thickness of groove 14: 0.003 inch Thickness of portions 18: 0.010 inch Thickness of portions 19: 0.020 inch Width of groove 14 (measured in direction of length of ribbon): 0.03 inch Length of each portion 18: 0.06 inch Length of each portion 19: 0.3 inch The cartridge fuse-link shown in FIG. 4 has a tubular ceramic container 40 provided with silver plated copper inner end caps 41. Each of these inner end caps is dished in the middle to form a recess illa which extends into the end of the tubular container 40. The outer cylindrical part 41b of each inner end cap is made with an internal diameter slightly less than the external diameter of tubular container 40, so that when forced thereon it grips with an interference fit.

The fuse-element 10, three of which are seen in FIG. 4, are inserted parallel to the axis of tubular container 40 and extend through central apertures 410 in the inner end caps. Their ends are bent outward at 10a and there soldered to the inner end caps 41.

When this stage of the assembly has been completed, an asbestos plug (not shown) is inserted to close the aperture 410 of one inner end cap, and the container 40 is filled from the other end with silica sand, a small portion of which is indicated diagrammatically at 42. Another asbestos plug (not shown) is then inserted to close the aperture Me of the other end cap.

The terminal members of the fuse-link each consist of a copper tag portion 43 and a copper disc portion 44. The exploded view in FIG. shows how these are con structed with a tongue 43a on the tag fitting closely into a slot 44a in the disc. The diameter of disc 44 is made slightly larger than the diameter of the recess 41a in the inner end cap so that, when inserted therein, it makes an interference fit.

A disc of solder (not shown) is inserted in the recess 41a of the inner end cap, followed by the disc part 44 of the assembled terminal member. Heat is then applied to melt the solder.

Finally, after all soldering has been completed and inspected, outer end caps 45 of silver plate copper, each having a slot 45a so that it will pass over tag 43, are pressed on with an interference fit over the inner end caps 41. This gives a neat finish to the cartridge, enclosing all the soldered junctions, and further tightens the frictional grip of the inner end caps 41 on the container 40.

The location of the solder filed trough of the element near one end of the element provides good heat conduction toward the relatively massive conductive members consisting of inner and outer end caps 41, 4d, copper disc 44 and tag 43, so that good and consistent cooling of this part of the element is ensured.

The fuse-element 10 in FIG. 5 differs from those in FIG. 4 in that the thickened end portions 16 and 17, shown in FIGS. 1 and 4, are omitted.

The inner end cap 41 of KG. 5 has, instead of a circular central aperture, a semi-circular aperture the straight side 41d of which passes through the axis of the container 40. The end 10a of the fuse-element 10 is turned over the straight side 41d of this aperture and soldered at 10a, and thus the fuse-element 10 is located centrally in the cartridge.

When more than about four fuse-elements are used in a fuse-link, provision is made to support some of them at each of two different radii from the axis of the cartridge. An example of an inner end cap 61 for this purpose is shown in FIG. 6. Here three fuse-elements 62 have their ends passed through a central circular aperture 61a, and are turned over and soldered as at 62a; whereas six more fuse-elements 63 have their ends passed through arcuate orifices 64 and have their ends turned over and soldered as at 63a. A good spacing of all the elements Within the container 40 is thus achieved.

FIG. 7 shows a multiple fuse-element in which four ribbons are united at both ends into single headers '70. The ribbons 10 are similar to the ribbon shown in FIG. 1 except that the thickened end portions 16 and 17 are absent, and that the solder troughs 11 are in this instance shown on the same face of the ribbons as are the grooves 14. Each of the headers '70 is shown with four tabs 70a intended to be individually turned down and soldered into an inner cap in the manner of fuseelernent ends 10a in FIG. 4. When inserted in a cartridge, the element shown in FIG. 7 may be bent into cylindrical or part-cylindrical form so that the ribbons 10 will be parallel to each other but not co-planar.

FIG. 8 shows another form of high current fuse-element consisting of a single wide ribbon having grooves 14 and solder-filled trough 15 similar to those in the element of FIG. 1. This element 80 is however intended for rolling into cylindrical form for insertion in a cartridge as shown in FIG. 9. The ends for turning down and soldering to the inner cap 41 are therefore each divided into a number of small tabs 80a which will extend radially.

The fuse-elements shown in FIGS. 1, 3, 7 and 8 are preferably manufactured by taking a sheet of silver, cutting the grooves, forming the trough and filling the trough with solder, and subsequently cutting the sheet perpendicularly to the grooves and trough so as to divide it into ribbons of the required width. The grooves and trough may be formed simultaneously by rolling the sheet between rollers as illustrated in FIG. 10.

What we claim as our invention and desire to secure by Letters Patent is:

l. A fuse-element comprising a ribbon of fusible metal, of uniform width, and having a series of grooves of reduced thickness each of which extends across the full width of the ribbon; said ribbon having also, at one end of said series of grooves, a transverse trough which extends across the full width of the ribbon, said trough being filled with metal of lower melting point than, and capable of alloying with, the metal of the ribbon.

2. A fuse-element comprising a ribbon of fusible metal, of uniforms width, and having a series of grooves of re duced thickness each of which extends across the full width of the ribbon; said ribbon having also, at one end of said series of grooves, a transverse trough which extends across the full width of the ribbon, said trough being filled with metal of lower melting point than, and capable of alloying with, the metal of the ribbon, said ribbon having uniform thickness between said grooves.

3. A fuse-element comprising a ribbon of fusible metal, of uniform width, and having a series of grooves of reduced thickness each of which extends across the full width of the ribbon; said ribbon having also, at one end of said series of grooves, a transverse trough which extends across the full width of the ribbon, said trough being filled with metal of lower melting point than, and capableof alloying with, the metal of the ribbon, said ribbon having uniform thickness between said grooves and also between said trough and its nearest groove.

References Cited in the file of this patent UNITED STATES PATENTS 6 Wood Jan. 12, 1943 Von Hoorn May 24, 1949 Jacobs Oct. 1, 1957 Lear ct. 15, 1957 Sugden Dec. 17, 1957 Simmonds Aug. 4, 1959 Kozacka June 7, 1960 Cox Sept. 20, 1960 Kozacka Oct. 31, 1961 

1. A FUSE-ELEMENT COMPRISING A RIBBON OF FUSIBLE METAL, OF UNIFORM WIDTH, AND HAVING A SERIES OF GROOVES OF REDUCED THICKNESS EACH OF WHICH EXTENDS ACROSS THE FULL WIDTH OF THE RIBBON; SAID RIBBON HAVING ALSO, AT ONE END OF SAID SERIES OF GROOVES, A TRANSVERSE TROUGH WHICH EXTENDS ACROSS THE FULL WIDTH OF THE RIBBON, SAID TROUGH BEING FILLED WITH METAL OF LOWER MELTING POINT THAN, AND CAPABLE OF ALLOYING WITH, THE METAL OF THE RIBBON. 